An adjustable camshaft assembly as set forth above, herein also termed an SCP (single cam phaser) camshaft, allows variable valve timing to be implemented in engines having different valves operated by lobes on the same camshaft. A phaser mounted on one end of the SCP camshaft allows the inner shaft and/or the outer tube to be rotated relative to a crankshaft driven pulley to permit the timing of at least one of the two groups of cam lobes to be altered in relation to the crankshaft timing.
There are numerous known types of phase change mechanisms, or phasers, some of which, for example vane-type phasers, are hydraulically operated. Within such phasers intended for use with a solid camshaft, it is known to incorporate a spring to bias the phaser into an extreme end position, to enable the engine to start and idle correctly while there is still insufficient oil pressure to operate the phaser. An example of such a phaser is described in US 2003/0217718.